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Black Medicare beneficiaries with implanted cardiac devices (ICDs) face a lower risk of atrial fibrillation (AF) than their white counterparts, despite a higher overall burden of vascular risk factors and a greater risk of stroke, researchers reported Feb. 11 in the Journal of the American Heart Association.

It’s well-established that blacks in the U.S. see a disproportionately higher risk of stroke compared to other racial groups, Monica L. Chen, BA, and co-authors wrote in the journal, and that disparity can be partially attributed to known differences in established risk factors. Some some major risk factors for stroke, though, like AF, might actually be less common in black populations.

“Prior studies have suggested that AF may be less common among blacks in the United States,” Chen, of the Feil Family Brain and Mind Research Institute at Cornell, et al. wrote. “It is unclear whether blacks truly have less AF or simply more undiagnosed AF.”

Chen and her team performed a retrospective cohort study of 47,417 patients using inpatient and outpatient CMS claims data from 2009 to 2015. Patients were aged 66 years and up and comprised a 5 percent nationally representative sample of Medicare beneficiaries.

All patients involved in the study had at least one documented Current Procedural Terminology code for interrogation of an implantable pacemaker, cardioverter-defibrillator or loop recorder, the authors said, and no history of AF, atrial flutter or stroke before their first device interrogation.

The team found that among all patients, the annual incidence of AF or atrial flutter was 12.2 per 100 person-years among blacks and 17.6 per 100 person-years among whites, (including Hispanics, Native Americans and Asians). Five years into follow-up, the incidence of AF or flutter was 33.7 percent among blacks and 44.4 percent among whites.

“The lower incidence of the composite endpoint of AF/atrial flutter reflected a lower risk of AF, while the risk of atrial flutter was similar in both groups,” Chen and co-authors wrote. “Despite the lower incidence of AF, a common and potent stroke risk factor, black patients had a significantly higher risk of stroke than non-black patients.”

The team said their results were robust across multiple sensitivity analyses. They said their findings build on past studies that have reported a lower incidence of AF among blacks, but the fact that their study was limited to older patients with ICDs means their findings can’t be extrapolated to other populations.

“We found that among Medicare beneficiaries with implanted cardiac devices capable of detecting atrial rhythm, black patients had a lower incidence of AF despite a higher incidence of ischemic stroke,” Chen et al. reported. “Further investigation of this paradox may elucidate novel mechanisms of cardioembolic stroke and reveal targets for reducing racial disparities in stroke risk.”